assertThat(firstCallable.called).isTrue();
    assertThat(secondCallable.called).isFalse();
    firstFuture.set(null);
    assertThat(secondCallable.called).isTrue();
  }

  public void testCancellationDoesNotViolateSerialization() {
    @SuppressWarnings({"unused", "nullness"})
    Future<?> possiblyIgnoredError = serializer.submitAsync(firstCallable, directExecutor());